A "space blanket" is a blanket designed to be used in emergency situations to reduce heat loss from a person's body. The blanket consists of a thin sheet of plastic material (often PET film) that is coated with a metallic reflecting agent, usually gold or silver in color, which reflects about 80% of the wearer's radiated body heat back to him or her.http://www.traditionalmountaineering.org/FAQ_SpaceBlankets.htm In the US, space blankets are made by vacuum depositing a very precise amount of pure aluminum vapor onto a very thin, durable film substrate. Space blankets are included in many emergency, first aid, and survival kits because they are usually waterproof and windproof.